Heavy Metals Research Articles

Impact of redox evolution of layered double hydroxides on the immobilization of structural and adsorbed heavy metals

Impact of redox evolution of layered double hydroxides on the immobilization of structural and adsorbed heavy metals

Response Surface Methodology: A Review on Optimization of Adsorption Studies

Herein, we reviewed response surface methodology (RSM), a powerful statistical tool widely used in optimizing adsorption processes to remove synthetic dyes, toxic heavy metals, and phenols from wastewater. The widely used RSM models during optimization are the central composite design and Box-Behnken, which are second-order polynomial models. The models give a predictive insight into the number of experimental runs to be carried out. Furthermore, an in-depth overview of RSM and its application in optimizing various adsorption parameters, such as adsorbent dosage, initial pollutant concentration, contact time, and pH is discussed. In addition, RSM enables researchers to efficiently determine the optimal conditions for maximum pollutant removal. Lastly, the findings of this research highlight the potential of RSM as a valuable tool for optimizing adsorption processes and contributing to sustainable water treatment technologies.

Simulated Experimental Study on the Removal of Methylene Blue-Cu(II) Composite Pollution by Magnetized Vaterite

The combined pollution of organics and heavy metals represents a significant environ-mental problem that has attracted widespread attention. This explores the treatment of methylene blue (MB) and Cu(II), which are common pollutants in dye wastewater, and the recycling of Cu. A magnetized vaterite (V-M) was synthesized using Bacillus velezensis, and its structure and magnetic performance were investigated. The effects and mechanisms of removing MB-Cu(II) composite pollution using V-M and H2O2 in combination were estimated. The results indicated that V-M is a combination of organic and inorganic substances, with 21.5 wt% organic matter and multiple organic functional groups, including O-H, -SH, and others. The combination of V-M and H2O2 can achieve a maximum removal percentage of 90% for MB-Cu(II) pollution. The analysis showed that MB was oxidized by the ·OH generated from the H2O2-based Fenton-like reaction, and was catalyzed by the Fe3O4 in V-M. The immobilization of Cu(II) by V-M was mostly realized through the binding of the organic substances on the surface of the V-M, multilayer adsorption, and a replacement reaction with Ca(II). Magnetic separation and the addition of diluted HCl were used for the recycling of the Cu(II) enriched by V-M, with a recycling percentage reaching 85%. This study introduced a novel approach to the remediation of MB-Cu(II) composite pollution, and the recycling of Cu(II).

Evaluation of Gender-Specific Variation in Lead-induced Nephrotoxicity in Wistar Rats

The kidney is sensitive to heavy metals because of its intensive metabolic activity and multiple functions namely those of excretion and pollutants concentration. The study aimed to evaluate the gender-specific variation in lead-induced nephrotoxicity in Wistar rats. 10 male and 10 female Wistar rats (180-220g) were each divided into 2 groups (n=5 each): Control (M), Lead alone (M), Control (F), Lead alone (F). Male and female rats of the experimental groups were administered a daily dose of 100 mg/kg/bw of lead acetate dispersed in distilled water for 21 days. All rats were anesthetized and sacrificed 24 hours after the last administration. Blood samples were collected via cardiac puncture for biochemical analysis, kidney tissues were harvested, homogenized, and analyzed for antioxidant enzymes (superoxide dismutase, catalase, glutathione peroxidase) and lipid peroxidation (measured by malondialdehyde levels). Results indicated a significantly (p<0.01) lower weight gain in the lead-only female (F) group compared to the lead-only male (M) group. Lead acetate exposure caused oxidative damage, evidenced by significantly reduced antioxidant enzyme levels and increased lipid peroxidation in both male and female groups, with the effects being more pronounced in females (p<0.05). Serum creatinine and Urea levels in the lead alone (M) and lead alone (F) group were increased when compared to their respective control groups (p<0.05) however serum creatinine was significantly (p<0.001) higher in lead alone (F) than lead alone (M). The electrolyte function increased significantly in this study (p<0.05) when compared with their control groups. Sodium ion in lead alone (F) increased significantly (p<0.01) when compared to lead alone (M). The study concludes that lead exposure induced nephrotoxicity in both male and female rats, but more significantly pronounced in females than the males. This increased severity may have been mediated by the higher lead-induced oxidative stress observed in the female rats compared to males.

Evaluation of environmental risks by heavy metals pollution and algae accumulations in two alpine lakes

Evaluation of environmental risks by heavy metals pollution and algae accumulations in two alpine lakes

Editorial: Safe utilization of heavy metals pollution in soils for healthy food

Editorial: Safe utilization of heavy metals pollution in soils for healthy food

Pollution characteristics and health risk assessment of heavy metals in PM2.5 in Fuxin, China.

Fuxin is located in the atmospheric channel around Bohai Bay, and its geographical location is very special. Few existing studies have investigated the pollution characteristics and health risk assessment of heavy metals in atmospheric PM2.5 during the four seasons in Fuxin, so a total of 180 PM2.5 samples were collected from four sampling sites in Fuxin from December 2021 to November 2022. The seasonal distribution characteristics of V, Cr, Mn, Co, Ni, Cu, Zn, Pb, As, Sb, Cd and Ba were analysed via inductively coupled plasma-mass spectrometry (ICP‒MS), and the source of the heavy metals was analysed via the enrichment factor (EF) and principal component analysis (PCA). A health risk model was used to assess the health risk of respiratory exposure in men, women and children in Fuxin. The results revealed that the annual average mass order of heavy metals in Fuxin PM2.5 was Zn (0.2947μg·m-3) > Pb (0.0664μg·m-3) > As (0.0225μg·m-3) > Ba (0.0205μg·m-3) > Mn (0.0187μg·m-3) > Cu (0.0140μg·m-3) > Cr (0.0095μg·m-3) > V (0.0067μg·m-3) > Ni (0.0061μg·m-3) > Sb (0.0024μg·m-3) > Cd (0.0019μg·m-3) > Co (0.0007μg·m-3). The annual average concentration of As was 3.75 times the GB3095-2012 (China) secondary standard limit, and the concentration of hazard quotient (HQ) in PM2.5 was lower than 1, but the concentration of incremental lifetime cancer risk (ILCR) in As was higher than the cancer risk threshold (10-4). These findings indicate a certain risk of cancer in the urban population of Fuxin. Therefore, it is necessary to control the emissions created from coal burning to minimize the health risks to the people of Fuxin.

Role of SiO2, TiO2, and Fe3O4 adsorbed on glycine for remediation of heavy metals and antibacterial activity in water.

Metals have a tendency to accumulate in the environment and can have carcinogenic effects. Accordingly, this study used density functional theory (DFT) calculations to investigate the adsorption of different metal ions on the glycine surface. Glycine has attracted a lot of research interest because of its remarkable metal-binding properties and cost effectiveness. Accordingly, to improve glycine's adsorption capacity, it has been combined with SiO2, TiO2, and Fe3O4, creating a glycine-metal oxide nanocomposite through hydrogen bonding. After optimizing the structures at their energy minima at the B3LYP/6-31G(d, p) level of theory, the following analyses were carried out: total dipole moment (TDM), frontier molecular orbitals (FMOs), reactivity indexes, and molecular electrostatic potential (MESPs). The study of TDM, FMOs, reactivity indexes, density of states (DOS), and UV-Vis absorption analysis demonstrated the improved reactivity of glycine due to functionalization with SiO2. Additionally, the results showed that, compared to the glycine, the glycine/SiO2 surface experiences a greater degree of charge redistribution as a result of more hydrogen bonds being formed with adsorbate molecules. Thus, the study successfully extracted Cr, Fe, Co, Ni, Cu, As, Cd, and Pb from wastewater by demonstrating their selectivity for the glycine/SiO2 nanocomposite. The findings show that Ni had a stronger adsorption for glycine/SiO2 than the others as TDM increased (34.040 Debye), band gap energy decreased significantly (0.249eV), and reactivity indices got improved. Additionally, the IR spectra were calculated and compared to the experimental data, which revealed remarkable frequency changes due to intermolecular interactions. HR-TEM scans validated the dispersion of SiO2 NP on the glycine surface with minimal aggregation. Furthermore, the antibacterial activity of glycine-amino acid-based surfactants was assessed, and the results show that glycine/SiO2 nanocomposites exhibited antibacterial efficacy against Gram-positive and Gram-negative microorganisms. These findings highlight the glycine/SiO2 nanocomposites for remediation of heavy metals and have antibacterial activity for treating pathogenic bacteria.

Experimental and molecular dynamic simulation studies of landfill contaminated groundwater remediation by graphene oxide coated zeolite

ABSTRACT Graphene oxide (GO) has proven effective in wastewater treatment due to its capability to adsorb heavy metals and organic contaminants. Zeolite is also widely used in contaminant remediation as a reactive material in permeable reactive barrier (PRB). Experimental column flow-through tests were applied in this study to investigate the remediation ability of composite granule-graphene oxide coated zeolite (GOZ) on FA, Pb2+ and NH4 +, from municipal landfill contaminated groundwater. Microscopic characterization and molecular dynamic simulation were carried out in sequence to understand the adsorption process. The results demonstrated that GO significantly enhanced zeolite’s adsorption capacity for Pb2+ and FA by 147.5% and 164.8%, respectively, though NH4 + removal experienced a slight decrease of 25% after GO coating. The ion exchange of Pb2+ resulted in more significant partial collapse compared to NH4 + due to different effective diameter comparing with the channel size of zeolite. However, GO coating relieved the framework deformation by engaging in functional group reactions during Pb2+ adsorption. A recommended surface area coating ratio between 47.0% and 78.4% was identified, as values outside this range may lead to significant GO deformation or inefficient FA adsorption. The GO-zeolite granules displayed significant potential in remediating various contaminants while effectively preventing GO aggregation and zeolite collapse. As technological advancements reduce GO production costs, the economic feasibility of using GOZ in groundwater remediation is increasingly promising.

Arsenic Enhances the Degradation of Middle-Chain Petroleum Hydrocarbons by Rhodococcus sp. 2021 Under Their Combined Pollution

The efficient and green remediation of petroleum hydrocarbon (PH) contamination has emerged as a viable strategy for environmental management. Here, we investigated the interaction between arsenic and PH degradation by Rhodococcus sp. 2021 under their combined pollution. The strain exhibited disparate responses to varying concentrations and valences of arsenic. The elevated concentration of arsenic (>100 mg/L) facilitated the degradation of PHs, and there was a positive correlation between arsenic-promoted degradation of PHs and their carbon-chain length. The degradation of PHs changed with arsenic conditions as follows: trivalent arsenic groups > pentavalent arsenic groups > arsenic-free groups (control). Arsenite and arsenate significantly promoted the gene expression of arsenic metabolism and alkane degrading. But unlike arsenite, arsenate also significantly promoted the gene expression of phosphate metabolism. And arsenite promoted the up-regulation of the expression of genes involved in the process of PHs oxidation and fatty acid oxidation. These results highlight the potential of Rhodococcus sp. 2021 in the remediation of combined total petroleum hydrocarbon (TPH) and heavy metal pollution, providing new insights into the green and sustainable bioremediation of combined pollution of organic matters such as PHs and heavy metals/heavy metal-like elements such as arsenic.

Determination of priority control factors for risk management of heavy metal(loid)s in park dust in Mianyang City

In order to determine the priority control elements and sources of heavy metal(loid)s (HMs) pollution in park dust, this study collected dust samples from 25 parks in the urban area of Mianyang City and measured the contents of 10 HMs. Based on Monte Carlo simulation, the probabilistic pollution levels and ecological-health risks of HMs were assessed. We found that the average contents of Zn, Co, Pb, and Cr were much higher than their background values in local soil and were influenced by artificial activities. The pollution assessment found that 5 parks were moderately polluted. The comprehensive pollution of HMs in the dust was mainly caused by Zn and Cr, and industrial source was the main contributor to Zn and Cr pollution. The contribution of As, Co, and Pb to the comprehensive ecological risk was high, accounting for 54.6%. Co, Pb, and As were the priority control HMs of ecological risk, while mixed source and industrial source were the priority control sources. HMs presented potential carcinogenic health risks to both children and adults. The non-carcinogenic risk to adults was within safety level, while some parks showed non-carcinogenic risk to children, which should be paid attention to. The source-specific health risk assessment showed that Cr and As were the priority control HMs for human health, while mixed source and industrial source were the priority control sources.

Water Quality Assessment and Prevalence of Waterborne Diseases within Chikun Local Government Area, Kaduna State-Nigeria

Study’s Excerpt Water quality and the prevalence of waterborne diseases in Chikun Local Government Area, Kaduna State, were assessed. Microbiological analyses revealed microbial, helminth and protozoan contamination in water sources while Physicochemical analyses revealed heavy metal contamination. There is a need for enhanced water treatment and community awareness for improving water safety and public health in the region. Full Abstract The health and well-being of individuals in a nation are intrinsically tied to the quality of water available for consumption. Access to high-quality water plays a vital role in supporting proper nutrition, ensuring food security, and preventing waterborne diseases. Therefore, this study was carried out to assess water quality and prevalence of waterborne diseases within Chikun Local Government Area, Kaduna State. A cross-sectional study was conducted between January and June 2024. Data were collected through the administration of questionnaires (400 respondents) and laboratory water analysis. Water samples were analyzed from various sources involving boreholes, rivers and wells through composite sampling and physicochemical and microbiological analyses. Results showed samples from Unguwan Maigero and Tricania possessed varying physicochemical properties, while water from Goningora and Nasarawa revealed high turbidity and heavy metal contamination. Chloride levels were below 500 ppm, and sulphate concentrations ranged from 10.76 to 378.3 ppm. Sodium levels ranged from 19.5 to 110 mg/l, and potassium levels exceeded the permissible limit in some samples. Total coliform counts exceeded national limits (zero coliform per 100ml of water), indicating significant microbial contamination. Parasitological analysis indicated helminths and protozoan contamination in non-borehole sources. Findings showed 41% prevalence of waterborne diseases with diarrhea and typhoid. The study indicates that community awareness, appropriate water treatment, surveillance, and monitoring are essentials for assuring the availability and utilisation of safe and high-quality drinking water in Chikun LGA, Kaduna State.

Application of a magnetic graphene nanocomposite modified with 5-aminoisophthalic acid amine group for chromium (VI) adsorption from aqueous solutions: kinetic and thermodynamic studies

ABSTRACT Polymer nanocomposites are composite materials that incorporate nanomaterials, such as magnetic graphene oxide (mGO), into a polymer matrix. To enhance its adsorption capacity, the surface of mGO nanoparticles was polymerised by a 5-aminoisophthalic acid amine group (mGO-AIPA) through a simplified co-precipitation method. The structural and morphological characteristics of the synthesised nanoparticles were evaluated through techniques such as X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FTIR), Field emission scanning electron microscopy (FESEM), Thermogravimetric analysis (TGA), and Vibrating sample magnetometer (VSM). Response surface method (RSM) was used to evaluate the effectiveness of mGO-AIPA nanocomposite in removing chromium (VI) ions by examining variables such as solution of pH, contact time, adsorbent dose and initial concentration. Also, the study of kinetic models, adsorption isotherms and thermodynamic modelling of the process were evaluated. The results found that the mGO-AIPA nanocomposite has the maximum removal of chromium (VI) ions from the aqueous solution by 83.11% in optimal conditions including pH 3.5, contact time of 35 min, an adsorbent dosage of 25 mg g−1 and an initial concentration of 55 mg L−1. The pseudo-second-order kinetic and Langmuir isotherm models had a better fit with the experimental data of adsorption and the maximum adsorption capacity of chromium (VI) the base of the Langmuir model was 90.91 mg g−1. Moreover, the thermodynamic analysis indicated that the process was exothermic and nonspontaneous process, implying that it was energetically unfavourable. These findings suggest that the mGO-AIPA nanocomposite has a high performance as an effectual adsorbent to eliminate chromium heavy metal from an aqueous medium.

Quantitative Assessment of Human Health Risks Associated with Heavy Metal and Bacterial Pollution in Groundwater from Mankweng in Limpopo Province, South Africa

Heavy metal and microbial pollution in groundwater raises health concerns due to its adverse effects. This study aimed to assess the health risks associated with heavy metal and bacterial pollution in groundwater in Mankweng. Heavy metals and Escherichia coli were detected using inductively coupled plasma mass spectrophotometry and a Colilert system, respectively. The heavy metal pollution index (HPI) and non-carcinogenic and carcinogenic risks were computed. The β-Poisson dose–response model was employed to predict the probability of E. coli infection. The metals’ concentrations were all within the permissible limits of the South African National Standard (SANS). However, Pb levels at sites E and G exceeded the World Health Organization (WHO) guideline (≤0.01 mg/L). HPI values were all less than 100, indicative of low contamination. The hazard quotient values were all less than 1, except for vanadium. The cumulative cancer risk ranged between 3.06 × 10−5 and 1.81 × 10−4 and between 3.55 × 10−5 and 2.20 × 10−4 for adults and children, respectively. E. coli was only detected at site L. The annual risk of E. coli infection exceeded the WHO risk limit of 10−4. The results underscore the need for the regular monitoring of groundwater.

Ecological Risk of Heavy Metals in an Eco-Industrial Park in China

ABSTRACT To ascertain whether rapid industrialization has affected the accumulation of heavy metals (HMs) in Suzhou Industrial Park (SIP), China, the occurrence and ecological risk of HMs, including Cu, Zn, Pb, Cr, Cd, Ni, As and Hg in sediments were analyzed. The results indicated that total concentrations of HMs (mg kg−1) were in the descending sequence of Zn (235.28) > Cr (95.71) > Cu (78.91) > Ni (55.51) > Pb (23.96) > As (22.12) > Cd (0.38) > Hg (0.14). The concentrations of HMs, except for Ni and Cd, were found to be below the probable effect level (PEL). Correlation analysis (CA) and principal component analysis (PCA) showed that HMs in SIP mainly originated from anthropogenic activities. HMs were mainly in residual fractions (55.5 ~ 95.1%), and the exchangeable fractions of Zn and Cd were relatively high. The risk assessment results indicated that Hg and Cd significantly contributed to ecological risks, whereas Cr and Pb made relatively minor contributions. Our findings indicated that intense anthropogenic activities promote HMs accumulations in streams in SIP during rapid industrialization.

A Decade-Long Comparison of Heavy Metal(loid)s in the River and Children’s Health Risk Assessment of an E-Waste Recycling Area

Informal e-waste recycling can cause serious heavy metal(loid) pollution to nearby bodies of water, thereby increasing the risk of heavy metal exposure to local residents. This study investigates metal(loid) pollution levels in the Lianjiang River, which flows through Guiyu, an e-waste recycling town in Shantou, Guangdong. In 2009 and 2020, water samples from the Lianjiang River were taken, and the levels of 12 metal(loid)s (V, Cr, Mn, Sr, Ni, Cu, Zn, As, Se, Cd, Ba, and Pb) were measured by ICP-MS. In total, 380 valid questionnaires from Guiyu kindergarten children were selected to assess child health. Exposure health risks for children were calculated using two forms of exposure (dermal and inhalation) and statistical methods (multiple linear regression and Bayesian kernel machine regression—BKMR). The concentrations of Mn, Ni, Pb, and Cd in 2009 were significantly higher than those in 2020. The concentration of heavy metal(loid)s had been decreasing in 2020. The non-carcinogenic risk levels of the 12 metal(loid)s in both exposure routes were at an acceptable risk level. The average carcinogenic risk levels for As, Cr, Ni, Pb, and Cd exceeded the ILCRi <10–6 acceptable range. According to MLR, it was found that daily oral intake doses of Pb [β(95% CI): −0.949 (−1.596, −0.863), p < 0.001 and Se [β(95% CI): −0.911 (−1.888, −0.092), p = 0.031] were negatively associated with body mass index. A BKMR model was developed, through which the synergistic effects of co-exposure to 12 heavy metal(loid)s on growth and development indicators in children were analyzed. Concentrations of heavy metal(loid)s in rivers near e-waste recycling sites have been decreasing for 10 years. It was found that the growth and development of children are affected by the intake of heavy metal(loid)s in water. The reduction in heavy metal(loid) contamination in e-waste recycling areas needs to be continued, and concern about its impact on children’s health must remain.

Appraisal of Heavy Metal Risk Hazards of Eisenia fetida-Mediated Steel Slag Vermicompost on Oryza sativa L.: Insights from Agro-Scale Inspection and Machine Learning Analytics

The steel industry drives world economic growth, yet it generates heavy metal-rich steel slag, which jeopardizes the environment. The utilization of vermi-technology is essential for the sustainable transformation of toxic steel waste slag (SW) into organic amendments, although field-scale use of vermiprocessed SW remains unexplored. To bridge the gap, this study evaluated the efficacy of vermiprocessed SW as an organic supplement for rice field cultivation, focusing on heavy metal (HM) bioavailability, human health risk, and yield in comparison to raw slag and NPK fertilizer. The results indicated a considerable decrease in the bioavailable fraction of heavy metals in T4 (1:1 SW vermicompost 50% + 50% fertilizer). In treatments, T9 (100% SW) and T10 (50% SW + 50% fertilizer) (FIAM) free ion activity modeling confirmed grain absorption of HMs, and the FIAM HQ values indicated the health risk for the direct application of steel slag waste on the field. The risk factor evaluation of HMs’ presence in treatments T9 and T10 established the possible cancer risk for living beings. Similarly, machine learning models like SOBOL sensitivity analysis and artificial neural networks revealed potential threats associated with HMs on different treatments, respectively. The correlation coefficient revealed the negative effects of bioavailable HMs on various soil microbial and enzymatic properties. Moreover, the abundant yield of rice was attributed to the combination treatment (1:1 50% + NPK 50%), which paved the way for an alternative agronomic approach based on the utilization of vermicomposted steel waste slag.

Antioxidants, ACE I Inhibitory Peptides, and Physicochemical Composition, with a Special Focus on Trace Elements and Pollutants, of SPRING Spawning Atlantic Herring (Clupea harengus) Milt and Hydrolysates for Functional Food Applications

Norwegian spring spawning (NVG) herring milt is a raw material with high nutritional and functional values. However, its incorporation into food presents physicochemical and sensory challenges. Its high DNA content, the presence of TMA/TMAO and possibly heavy metal and/or environmental pollutants, and its bitter taste due to amino acids or peptides requires a careful approach to food development. Hydrolysis with food-grade enzymes enable an improvement in both the functional and sensory properties of the substrate and the increased stability of the raw materials and end products. HLPC, GC-MS, and in vitro protocols were used for the characterisation of manually extracted material (sample code: HMC) and milt from a fish-filleting line from early spring/late autumn catches. Three different food-grade protein hydrolysates were prepared from these raw materials (sample codes: H1, H2, and H3) as a means to estimate their functional food development potential. Combinations of three commercial enzymatic preparations were applied, targeting specific sensory properties. Parameters related to consumer safety (e.g., the presence of heavy metals and TMA/TMAO); beneficial health effects, such as antioxidant or antihypertensive bioactivities (measured using in vitro TAC, ORAC, DPPH, and ACE I inhibitory activity assays); the presence of beneficial fatty acids and micronutrients; and the protein quality were studied. On the basis of their total amino acid compositions, freeze-dried herring milt and hydrolysates could provide high-quality protein with most of the essential amino acids and taurine. Powdered milt has a particularly high fatty acid profile of bioavailable omega-3 fatty acids (2024.06 mg/100 g docosahexaenoic acid (DHA; 22:6n-3) and 884 mg/100 g eicosapentaenoic acid (EPA; 20:5n-3)). The experimentally measured levels of arsenic (3.9 ± 1.2 mg/kg) and cadmium (0.15 ± 0.05 mg/kg) were higher than the levels of the other two heavy metals (mercury and lead). The bioactivity is concentration-dependent. Overall, this work presents complementary information for the future utilisation of C. harengus powdered milt (possibly obtained directly from a fish-filleting line) and some of its protein hydrolysates as food ingredients.

Impact of Acid Rain on Release Characteristics of Heavy Metals in Low-Sulfur Tailings with Strong Acid Neutralization Capacity: A Case Study from Northern Guangxi, China

Tailing ponds are major sources of heavy metal pollution. Previous studies primarily focused on tailings with high sulfur content, with limited attention to low-sulfur tailings. This study explored the release behavior of Pb, Zn, and Cd from low-sulfur tailings under simulated acid rain conditions, considering factors such as pH, particle size, and weathering degree. Samples were collected from a lead–zinc tailing pond in the karst regions of northern Guangxi, China. Batch leaching experiments indicated that even with high acid neutralization capacity (ANC = 166.57–167.45 kg H2SO4/t), substantial heavy metal leaching occurred under acidic conditions (pH 2–3), with Pb, Zn, and Cd concentrations increasing 4–6 times compared to neutral conditions. Leachate concentrations were slightly higher in coarser particles than in finer ones, while weathering further enhanced metal release, particularly for Cd. These findings suggest that acid neutralization alone may not be sufficient to prevent heavy metal leaching in low-sulfur tailings exposed to acid rain. However, due to the laboratory scale of this study, further validation through field-scale or mesocosm experiments is necessary to confirm the observed trends and assess their implications for environmental risk management in karst regions.

Efficient and sustainable approach of heavy metal adsorption from wastewater using algal biomass of Hypnea valentiae (Turner) Montagne, 1841

The biosorption of heavy metals especially, Cd2+, Pb2+, and Zn2+ from wastewater were evaluated using the biomass of macroalgae, Hypnea valentiae found in coastal waters of Rameshwaram, Tamil Nadu, India. The probable functional groups involved in the biosorption process was analyzed by Fourier transform infrared spectroscopy. The specific surface area, pore volume and pore diameter of prepared biosorbent was determined by Brunauer–Emmett–Teller (BET) analysis and it was found to be 59.993 m2 g−1, 0.292 cc g−1 and 1.429 nm, respectively. The scanning electron microscopy images after the biosorption revealed that the heavy metals have been adsorbed on to the surface of biosorbent. The optimization study was performed using Box–Behnken design and the optimum parameters used were initial concentration of metal ions (10–500 mg L−1), biomass dose (5–25 g L−1), contact time (10–120 min), temperature (25–45 °C), agitation speed (60–120 rpm) and pH (2–14). The heavy metal uptake (biosorption) was assessed by isotherm models including Dubinin–Radushkevich (D–R), Freundlich and Langmuir models. The maximum sorption of metal ions was observed in Langmuir isotherm model (R L 0.1773 and K F 2.2030 L mg−1) with an R 2 value close to 0.99 clearly indicating the chemical mode of metal ion adsorption. Also, the sorption of Cd2+, Pb2+, and Zn2+ on to the surface of algal biomass followed pseudo-second-order kinetics with a rate constant, k2 being 9.627 × 10−3 g (mg min) −1 and qe being 93.98496 mg g−1, strongly supporting the chemisorption mechanism. The computed thermodynamic parameters (ΔG°, ΔH, and ΔS) demonstrated an endothermic, spontaneous biosorption that was feasible. The maximum removal efficiency was achieved for Pb (92.86%) followed by Cd (91.48%) and Zn (87.32%). The biosorbent can be reused and regenerated up to four cycles efficiently. There was a significant reduction in the biological oxygen demand, chemical oxygen demand, total dissolved solids, and pH of wastewater after treatment with the biosorbent. From this study, it is assessed that the biomass from red algae can be utilized for the biosorption of heavy metals from polluted water which is cost-effective and eco-friendly.